Add notes on NO_COLOR environment variable to the manual

docs/content/manual/manual.yml

@@ -168,6 +168,8 @@ sections:
         By default, jq outputs colored JSON if writing to a
         terminal. You can force it to produce color even if writing to
         a pipe or a file using `-C`, and disable color with `-M`.
+        When the `NO_COLOR` environment variable is not empty, jq disables
+        colored output by default, but you can enable it by `-C`.
 
         Colors can be configured with the `JQ_COLORS` environment
         variable (see below).